Synthesis of Branched Polyethylene from Ethylene via in situ Copolymerization Catalyzed by β-Diketonate Zirconium/AlEt_2Cl/MAO

A novel catalytic system to prepare branched polyethylene with single catalyst activated by two different co-catalysts is reported in this paper via the tandem catalysis, with ethylene as single monomer. Such catalytic system is composed of beta-diketonate zirconium complexes, i.e. (acac) (2)ZrC1(2) (I) and (dbm)(2) ZrCl2 (II) as catalyst precursors, diethylaluminium chloride (AlEt2Cl) as a co-catalyst for ethylene oligomerization and methylaluminoxane (MAO) as another one for the in situ copolymerization with ethylene. The oligomers obtained were mainly alpha-olefins, and the contents of them in weight were 76.84% for I and 65.99% for II, while the part being able to be copolymerized was 62.12% and 55.32% for I and II, respectively. The branched polyethylene via in situ copolymerization of ethylene was prepared by the tandem catalytic system I/AlEt2 Cl/MAO or II/AlEt2 Cl/MAO. C-13 NMR spectrum reveals that the resultant copolymer was branched polyethylene with total branches of 2.1/1000C, including ethyl group of 1.2/1000C, butyl group of 0.8/ 10000 and longer branches of 0.1/1000C. With increasing the molar ratio of AlEt2Cl to MAO, the melting temperature of the polymer obtained decreased from 133.7 to 116.7 degrees C for I/AlEt2Cl/MAO and from 131.7 to 118.8 degrees C for II /AlEt2 Cl/MAO as well as the change of crystallinity. The catalytic activities for catalyst I /AlEt2Cl/MAO and II /AlEt2Cl/MAO were from 2.48 x 10(4) to 0. 10 x 10(4) g PE/ (mol Zr center dot h) and from 1.00 x 10(4) to 0.32 x 10(4) g PE/(mol Zr center dot h), respectively. The results indicate that the branched polyethylene can be obtained by such a catalytic system.